Gas filter, process for producing a gas filter and use of this gas filter

ABSTRACT

A gas filter, a process for producing a gas filter and the use of the gas filter are claimed. The filtration of gases, in particular of gases which are contaminated by solids, e.g. automobile exhaust gases, is difficult since the solids which have been filtered out block the filter over the course of time. The gas filter of the invention can be used over relatively long periods of time since it is regenerable.  
     The improvement achieved by the invention compared to conventional gas filters is that the filter comprises a composite material which can be heated in a simple manner by application of a voltage to the electrically conductive support material of the composite material and thermally decomposable substances Which can block the filter can be decomposed.  
     The filter of the invention can be used wherever gases which are contaminated by thermally decomposable solids have to be cleaned.

[0001] A gas filter, a process for producing a gas filter and use ofthis gas filter are claimed.

[0002] Air pollution is known to present a serious problem in many partsof the world. Depending on composition, the pollution can lead to healthproblems among the human population. Furthermore, the air pollutionresults in not inconsiderable economic loss. The air pollution can be inthe form of gases or of liquids dispersed very finely in the air or inthe form of tiny solid particles present in the air. The solid particleswhich may be present in the air and have been and are classified ascarcinogenic include soot, especially soot (particulates) which getsinto the air via the exhaust gases of diesel vehicles.

[0003] In many nations, regulations to regulate the maximum permissibleemission of particulates from motor vehicles have been put in force.

[0004] Various methods and apparatus have already been developed fortreating solids-containing gases.

[0005] U.S. Pat. No. 4,872,889 and U.S. Pat. No. 4,948,403 claim ceramicfilter systems which are able to filter soot or solid particles from theexhaust gases of diesel-powered vehicles.

[0006] A problem with these methods and apparatus is that the solidparticles block the filter relatively quickly and the filters thus haveto be replaced or regenerated at short intervals.

[0007] To regenerate blocked filters, there have been proposals formethods which burn the solids blocking the pores of the filter in motorvehicles by additional combustion of fuel. The disadvantage of thesemethods is that regeneration leads to an increased fuel consumption. Inaddition, the deep action of this method is only weak, so that blockagescaused by particles in the filter cannot be remedied.

[0008] More recently, methods and apparatus which remove filtered-outsolids from the filter by heating to 600° C. have been developed.

[0009] According to DE 3800723, additional heating wires are used forheating the filter.

[0010] EP 075372 uses heating elements comprising wire, expanded metalor perforated foils for heating the filter.

[0011] GB 2193656 teaches a method and an apparatus which make use ofwires between which a current flows when a conductive bridge ofdeposited soot forms.

[0012] U.S. Pat. No. 5,202,548 describes a filter which can be baked outby application of a voltage since it is equipped with electricallyconductive honeycomb structures. U.S. Pat. No. 5,246,672 teaches the useof woven wire meshes and U.S. Pat. No. 5,254,840 teaches the use of acombination metallic and ceramic honeycombs.

[0013] The filter materials used in the abovementioned methods orapparatus have relatively small surface areas and thus either a lowfilter action or, when she pores are made smaller to increase the filteraction, a small gas throughput. If the surface area is large due to theuse of porous materials, the pores become blocked very quickly.Filtering relatively large amounts of gas requires the use of large,relatively cumbersome gas filters which restricts the possible uses ofsuch gas filters.

[0014] It is therefore an object of the present invention to find aneconomical process for producing a gas filter which, despite a smallsize, is able to filter large amounts of gas and which can beregenerated in a simple manner.

[0015] It has surprisingly been found that a gas filter which comprisesa material-permeable composite material based on at least oneopen-structured and material-permeable support and having on at leastone side of the support and in the interior of the support at least oneinorganic component which comprises essentially at least one compound ofa metal, a semimetal or a mixed metal with at least one element of maingroups III to VII is able, even when small in size, to filter largeamounts of gas and can be regenerated in a simple manner.

[0016] The present invention accordingly provides a regenerable gasfilter for filtering gases which comprises a composite material based onat least one openstructured and material-permeable support and having onat least one side of the support and in the interior of the support atleast one inorganic component which comprises essentially at least onecompound of a metal, a semimetal or a mixed metal with at least oneelement of main groups III to VII.

[0017] The present invention likewise provides a regenerable gas filterwhich comprises a composite material which is obtainable by applicationof a suspension which comprises at least one inorganic componentcomprising a compound of at least one metal, a semimetal or a mixedmetal with at least one element of main groups III to VII and a sol toan open-structured and materialpermeable support and by subsequentheating at least once during which the suspension comprising at leastone inorganic component is solidified on or in or on and in the support.The present invention also provides a process for producing a gas filteras claimed in any of claims 1 to 40, which comprises producing amaterial-permeable composite material by applying, in and on at leastone open-structured and material-permeable support, at least onesuspension Which comprises at least one inorganic component comprisingat least one compound of at least one metal, a semimetal or a mixedmetal with at least one of the elements of main groups III to VII and asol and by solidifying the suspension on or in or on and in the supportmaterial by subsequent heating at least once.

[0018] The present invention likewise provides for the use of a gasfilter as claimed in any of claims 1 to 40 for cleaning waste or feedgases.

[0019] For the purposes of the present invention, materialpermeablemeans that materials which have this property are permeable to at leasta gas, a liquid or a solid. The permeability is dependent on the size ofthe pores, mesh openings or holes which these materials have.

[0020] The gas filter of the invention can be it used for the filtrationof any waste and feed gases from which, for example, solid particles areto be removed. The gases to be filtered can also comprise vapor ordroplets of liquid. The advantage of the gas filter of the invention isthat, as a result of the use of an electrically conductive supportmaterial in the composite material, the latter can be baked out in asimple manner by application of a voltage and thus be regenerated. Ifthe composite material comprises catalytically active materials, thisheating only has to be carried out once if the decomposition of thethermally decomposable liquid droplets or solid particles is, in thecase of a sufficiently hot filter, catalyzed by the catalytically activematerials and thus proceeds swiftly. As a result, advantageously, avirtually constant amount of gas can pass through the filter sinceblocking of the filter by materials which are not thermally decomposableincreases only very slowly.

[0021] A further advantage of the gas filter of the invention is thatthe novel composite material or gas filter can, due to the fact that itis bendable, be rolled or folded and the filter-active surface area ofthe filter can be very large in a small volume.

[0022] The gas filter of the invention is described below by way ofexample without being restricted thereby.

[0023] The regenerable gas filter of the invention for the filtration ofgases comprises at least one composite material based on at least oneopen-structured and material-permeable support and having on at leastone surface of the support and in the interior of the support at leastone inorganic component which comprises essentially at least onecompound of a metal, a semimetal or a mixed metal with at least oneelement of main groups III to VII. For the purposes of the presentinvention, interior of a support means, for example, hollow spaces orpores in a support. According to the invention, the regenerable gasfilter comprises a composite material which is obtained by applicationof a suspension which comprises at least one inorganic componentcomprising a compound of at least one metal, a semimetal or a mixedmetal with at least one element of main groups III to VII and a sol toan open-structured and material-permeable support and by heating atleast once during which the suspension comprising at least one inorganiccomponent is solidified on or in or else on and in the support.

[0024] According to the invention, the composite material or gas filtercan be permeable to gases, solids or liquids, in particular to particleshaving a size of from 0.5 nm to 10 μm.

[0025] A support having intermediate spaces having a size of from 50 to500 μm can advantageously be present in the composite material of thegas filter. This support can comprise woven or felted fibers, expandedmetal or sintered metal. The support preferably comprises at least oneat least partially electrically conductive material.

[0026] The intermediate spaces can be pores, mesh openings, holes,crystal lattice interstices or voids. The support can comprise at leastone material selected from the group consisting of carbon, metals,alloys, glass, ceramics, minerals, plastics, amorphous substances,natural products, composite materials or at least one combination ofthese materials. The supports which can comprise the abovementionedmaterials can have been modified by a chemical, thermal or mechanicaltreatment method or a combination of treatment methods. Preferably, thecomposite material comprises a support comprising at least one metal, anatural fiber or a plastic which has been modified by at least onemechanical forming technique or treatment method, e.g. drawing, swaging,fulling, rolling, stretching or forging. Very particularly preferably,the composite material comprises at least one support comprising atleast woven, bonded, felted or ceramically bound fibers or at leastsintered or bonded shaped bodies, spheres or particles. In a further,preferred embodiment, a perforated support can be used.Material-permeable supports can also be ones which become or have beenmade material-permeable by laser treatment or ion beam treatment.

[0027] It can be advantageous for the support to comprise fibers of atleast one material selected from the group consisting of carbon, metals,alloys, ceramics, glass, minerals, plastics, amorphous substances,composite materials and natural products or fibers of at least onecombination of these materials, e.g. asbestos, glass fibers, rock woolfibers, carbon fibers, metal wires, steel wires, polyamide fibers,coconut fibers or coated fibers. Preference is given to using supportswhich comprise at least woven fibers of metal or alloys. Wires can alsoserve as metal fibers. The composite material very particularlypreferably comprises a support comprising at least one woven mesh ofsteel or stainless steel, e.g. woven meshes produced from steel wires,steel fibers, stainless steel wires or stainless steel fibers byweaving, which preferably has a mesh opening of from 5 to 500 μm,particularly preferably mesh openings of from 50 to 500 μm and veryparticularly preferably mesh openings of from 70 to 120 μm.

[0028] The support of the composite material can, however, also compriseat least one expanded metal having a pore size of from 5 to 500 μm.According to the invention, the support can also comprise at least onegranular, sintered metal, a sintered glass or a metal nonwoven having apore width of from 0.1 μm to 500 μm, preferably from 3 to 60 μm.

[0029] According to the invention, the composite material preferablycomprises a support comprising at least aluminum, silicon, cobalt,manganese, zinc, vanadium, molybdenum, indium, lead, bismuth, silver,gold, nickel, copper, iron, titanium, platinum, stainless steel, steel,brass, an alloy of these materials or a material coated with Au, Ag, Pb,Ti, Ni, Cr, Pt, Pd, Rh, Ru and/or Ti.

[0030] The inorganic component present in the composite material or gasfilter can comprise at least one compound of at least one metal,semimetal or mixed metal with at least one element of main groups III toVII of the Periodic Table or at least one mixture of these compounds.Here, the compounds of the metals, semi-metals or mixed metals cancomprise at least elements of the transition series and main groups IIIto V or at least elements of the transition series or main groups III toV, with these compounds having a particle size of from 0.001 to 25 μm.The inorganic component preferably comprises at least one compound of anelement of main groups III to VIII or at least one element of maingroups III to V with at least one of the elements Te, Se, S, O, Sb, As,P, N, Ge, Si, C, Ga, Al or B or at least one compound of an element ofmain groups III to VIII and at least one element of main groups III to Vwith at least one of the elements Te, Se, S, 0, Sb, As, P, N, Ge, Si, C,Ga, Al or B or a mixture of these compounds. Particularly preferably,the inorganic component comprises at least one compound of at least oneof the elements Sc, Y, Ti, Zr, V, Nb, Cr, Mo, W, Mn, Fe, Co, B, Al, Ga,In, Tl, Si, Ge, Sn, Pb, Sb or Bi with at least one of the elements Te,Se, S, O, Sb, As, P, N, C, Si, Ge or Ga, e.g. TiO_(1,) Al₁ O₃,ZrO, Y₂O₃,BC, SiC, Fe₃O₂, SiN, SiP, nitrides, sulfates, phosphides, silicides,spinels or yttrium-aluminum garnet or one of these abovementionedelements itself. The inorganic component can also comprisealuminosilicates, aluminum phosphates, zeolites or partially exchangedzeolites such as ZSM-5, Na-ZSM-5 or Fe-ZSM-5 or amorphous microporousmixed oxides which may contain up to 20% of non-hydrolyzable organiccompounds, e.g. vanadium oxide-silicon oxide glass or aluminumoxidesilicon oxide-methylsilicon sesquioxide glasses.

[0031] Preferably at least one inorganic component is present as aparticle size fraction having a particle size of from 1 to 250 nm orhaving a particle size of from 260 to 10,000 nm.

[0032] It can be advantageous for the composite material to comprise atleast two particle size fractions of at least one inorganic component.The particle size ratio of the particle size fractions in the compositematerial is from 1:1 to 1:10,000, preferably from 1:1 to 1:100. Thecomposite material particularly preferably comprises at least oneparticle size fraction having an average particle size of from 0.3 to 3μm. The ratio of the amounts of the particle size fractions in thecomposite material is preferably from 0.01:1 to 1:0.01.

[0033] The material permeability of the composite material can belimited to particles having a particular maximum size by means of theparticle size of the inorganic component used. It can be advantageousfor the composite material to have pores which are permeable toparticles having a maximum size of from 0.1 to 10 μm, particularlypreferably a maximum size of from 0.2 to 1.5 μm.

[0034] The suspension which comprises at least one inorganic componentand by means of which the composite material of the invention can beobtained can comprise at least one liquid selected from the groupconsisting of water, alcohol and acid or a combination of these liquids.

[0035] In a further particular embodiment of the gas filter of theinvention, the composite material comprises at least one catalyticallyactive component. The catalytically active component can be identicalwhen the inorganic component. This applies particularly when theinorganic component has catalytically active centers on the surface.

[0036] The catalytically active component present in the compositematerial is preferably at least one inorganic material, at least onemetal or at least one organometallic compound which has catalyticallyactive centers on its surface. The catalytic component present in thecomposite material is particularly preferably a zeolite such as ZSM-5,Fe-ZSM-5, silicalite or an amorphous microporous mixed oxide asdescribed, for example, in DE 195 45 042 and/or DE 195 e.g. vanadiumoxide-silicon oxide glass or aluminum oxidesilicon oxide-methylsiliconsesquioxide glasses.

[0037] The composite material can, however, also comprise at least oneoxide of at least one of the elements Mo, Sn, Zn, V, Mn, Fe, Co, Ni, As,Sb, Pb, Bi, Ru, Re, Cr, W, Nb, Hf, La, Ce, Gd, Ga, In, Tl, Ag, Cu, Li,K, Na, Be, Mg, Ca, Sr and Ba as catalytically active component.

[0038] In a particular embodiment of the material-permeable compositematerial, this comprises at least titanium suboxide as catalyticallyactive component.

[0039] It can likewise be advantageous for the composite material tocomprise, as catalytically active component, at least one metal compoundselected from among the compounds of the metals Pt, Rh, Ru, Ir, Au, Ag,Os, Re, Cu, Ni, Pd and Co, or at least one metal selected from among themetals Pt, Rh, Ru, Ir, Au, Ag, Os, Re, Cu, Ni, Pd and Co.

[0040] Particularly preferred catalytic components are, for example,noble metals, noble metal compounds or materials coated with noble metalparticles. The addition of the catalytically active component makes itpossible to achieve a situation where the filter becomes blocked moreslowly after heating once due to catalytic decomposition of thermallydecomposable solids or liquids, since only particles which cannot bedestroyed thermally block the filter. This particular embodiment enablesthe operating life of the filter of the invention to be increasedconsiderably.

[0041] In a particularly preferred embodiment of the gas filter orcomposite material of the invention, this can be made bendable withoutdestruction of the inorganic component solidified in the interior of thesupport and on the support. The composite material of the invention ispreferably able to be bent to a smallest radius down to 1 mm.

[0042] Preferably, the composite material in the gas filter is rolled orfolded in a suitable container having at least one gas inlet and atleast one gas outlet, with the composite material being arranged so thatthe gas to be filtered has to pass, after entering the gas filter, atleast once through the composite material before it can leave the gasfilter via the gas outlet.

[0043] In one variant of the gas filter of the invention, thermallydecomposable or sublimable or vaporizable solids or liquids which havebeen filtered from a filtered gas and block the pores of the compositematerial, e.g. soot or hydrocarbon particles, can be removed from thegas filter by baking out the gas filter by application of a voltage tothe support of the composite material. Depending on the selected supportmaterial, preferably a support material having a low electricalresistance, the filter can be heated using a low voltage as iscustomary, for example, in motor vehicles, e.g. 12 or 24 V. It can beadvantageous for the gas inlet and the gas outlet to be provided with aflow- or pressure-measuring device by means of which the pressure or theamount of the gas entering and leaving the filter is measured and forthe heating of the gas filter to be commenced on reaching a presetdifference between the measured values, which represents a measure ofthe blocking of the composite material.

[0044] The process of the invention for producing the gas filter of theinvention is described below, without being restricted thereto.

[0045] The gas filter of the invention can be produced by producing amaterial-permeable composite material by applying, in and/or on at leastone open-structured and material-permeable support, at least onesuspension which comprises at least one inorganic component comprisingat least one compound of at least one metal, a semimetal or a mixedmetal With at least one of the elements of main groups III to VII and asol and by solidifying the suspension on or in or on and in the supportmaterial by subsequent heating at least once.

[0046] When carrying out the process of the invention, it can beadvantageous to apply the suspension on and in or else on or in at leastone support by printing, pressing-on, pressing-in, rolling-on, doctorblade coating, painting-on, dipping, spraying or casting.

[0047] The open-structured and material-permeable support can comprise amaterial selected from the group consisting of carbon, metals, alloys,ceramics, glass, minerals, plastics, amorphous substances, naturalproducts, composite materials or at least one combination of thesematerials. The preferred support is a woven stainless steel or steelmesh.

[0048] The suspension used, which comprises at least one inorganiccomponent and at least one metal oxide sol, at least one semimetal oxidesol or at least one mixed metal oxide sol or a mixture of these sols,can be produced by suspending at least one inorganic component in atleast one of these sols. It can be advantageous for the suspension tocomprise at least one catalytically active component. The catalyticallyactive component can be identical to the inorganic component.

[0049] The sols are obtained by hydrolyzing at least one metal compound,at least one semimetal compound or at least one mixed metal compoundusing a liquid, a gas or a solid. It can be advantageous for the liquidused for hydrolyzing the compound to be hydrolyzed to be water, alcoholor an acid or a combination of these liquids or the solid used to be iceor the gas used to be water vapor. It can likewise be advantageous forthe compound to be hydrolyzed to be added prior to the hydrolysis to atleast one alcohol or at least one acid or a combination of theseliquids. As compound to be hydrolyzed, preference is given tohydrolyzing at least one metal nitrate, a metal chloride, a metalcarbonate, a metal alkoxide compound or at least one semimetal alkoxidecompound, particularly preferably at least one metal alkoxide compound,a metal nitrate, a metal chloride, a metal carbonate or at least onesemimetal alkoxide compound selected from among the compounds of theelements Ti, Zr, Al, Si, Sn, Ce and Y or the lanthanides and actinides,e.g. zirconium alkoxide, silicon alkoxide or titanium alkoxidecompounds, e.g. titanium isopropoxide, silicon alkoxides, zirconiumalkoxides, or a metal nitrate such as sirconium nitrate.

[0050] It can be advantageous to carry out the hydrolysis of thecompounds to be hydrolyzed using at least half the molar ratio of water,water vapor or ice, based on the hydrolyzable group, of the hydrolyzablecompound.

[0051] The hydrolyzed compound can be peptized by treatment with atleast one organic or inorganic acid, preferably a 10-60 strength organicor inorganic acid, particularly preferably a mineral acid selected fromthe group consisting of sulfuric acid, hydrochloric acid, perchloricacid, phosphoric acid and nitric acid and mixtures of these acids.

[0052] It is possible to use not only sols which have been prepared asdescribed above but also commercial sols such as titanium nitrate sol,zirconium nitrate sol or silica sol. It can be advantageous if at leastone inorganic component having a particle size of from 1 to 10,000 nm issuspended in at least one sol. Preferably, an inorganic componentcomprising at least one compound selected from among metal compounds,semimetal compounds, mixed metal compounds and metal mixed compoundswith at least one of the elements of main groups III to VI, or at leastone mixture of these compounds, is suspended. Particularly preferably,at least one inorganic component comprising at least one compoundselected from among the oxides of the transition elements or theelements of main groups III to V, preferably oxides selected from amongthe oxides of the elements Sc, Y, Ti, Zr, Nb, Ce, V, Cr, Mo, W, Mn, Fe,Co, B, Al, In, Tl, Si, Ge, Sn, Pb and Bi, for example Y₂O₃, ZrO, Fe₁O₃,Fe₂O₃, SiO, Al₂O₃, is suspended.

[0053] The proportion by mass of the suspended component is preferablyfrom 0.1 to 500 times that of the hydrolyzed compound used.

[0054] In a particular variant, the sol used is preferably titaniumdioxide sol acidified with mineral acid and/or the inorganic componentused is preferably aluminum oxide having a particle size of from 0.3 to3 μm.

[0055] It can be advantageous for at least one catalytically activecomponent, e.g. a noble metal or a noble metal compound, to be added tothe sol and to be incorporated into the gas filter or the compositematerial. It can likewise be advantageous for at least one catalyticallyactive component having a particle size of from 1 to 10,000 nm to besuspended in a sol. Preferably, at least one catalytically activecomponent comprising at least one compound selected from among metalcompounds, semimetal compounds, mixed metal compounds and metal mixedcompounds with at least one of the elements of main groups III to VII ororganic compounds, or at least one mixture of these compounds, issuspended. Particularly preferably, at least one catalytically activecomponent comprising at least one compound selected from amongaluminosilicates, aluminum phosphates, zeolites or partially exchangedzeolites, e.g. ZSM-5, Na-ZSM-5 or Fe-ZSM-5, and amorphous microporousmixed oxides which may contain up to 20 of non-hydrolyzable organiccompounds, e.g. vanadium oxide-silicon oxide glass or aluminumoxide-silicon oxide-methylsilicon sesquioxide glasses, is suspended.

[0056] The proportion by mass of the suspended components is preferablyfrom 0.1 to 500 times that of the hydrolyzed compound used.

[0057] Appropriate selection of the particle size of the suspendedcompounds as a function of the size of the pores, holes or intermediatespaces of the openstructured material-permeable support, but also thelayer thickness of the composite material of the invention and thesol-solvent-metal oxide ratio, enable the freedom from cracks of the gasfilter of the invention or the composite material to be optimized.

[0058] When using a woven mesh having a mesh opening of, for example,100 μm, it is possible to increase the freedom from cracks by using,preferably, suspensions which comprise a suspended compound having aparticle size of at least 0.7 μm. In general, the ratio of particle sizeto mesh opening or pores should be from 1:1000 to 50:100. The compositematerial of the invention preferably has a thickness of from 5 to 1000μm, particularly preferably from 50 to 150 μm. The suspension comprisingsol and compounds to be suspended preferably has a weight ratio of solto compounds to be suspended of from 0.1:100 to 100:0.1, preferably from0.1:10 to 10:0.1.

[0059] According to the invention, the suspension present on or in orelse on and in the support can be solidified by heating the composite atfrom 50 to 1000° C. In a particular variant, the composite is subjectedto a temperature of from 50 to 100° C. for from 10 minutes to 5 hours.In a further particular variant, the composite is subjected to atemperature of from 100 to 800° C. for from 1 second to 10 minutes.

[0060] The composite can be heated by means of heated air, hot air,infrared radiation, microwave radiation or electrically generated heat.In a particular embodiment of the process of the invention, it can beadvantageous for heating to be carried out using the support material aselectric resistance heating element. For this purpose, the support canbe connected via at least two contacts to a power source. Dependingon-the power of the power source, the voltage which is applied and theintrinsic resistance of the electrically conductive support, the supportheats up when the power is switched on and the suspension present in andon the support can be solidified thereby.

[0061] In a further, preferred embodiment of the process of theinvention, solidification of the suspension can be achieved by thesuspension being applied on or in or else on and in a preheated supportand thus being solidified directly after application. In a further,particular embodiment of the process of the invention, it can beadvantageous for at least one support to be unwound from a roll, passedat a speed of from 1 m/h to 1 m/s through at least one apparatus whichapplies the suspension on or in or on and in the support and at leastone further apparatus which makes possible the solidification of thesuspension on or in or on and in the support by heating and thecomposite material thus produced is wound up on a second roll. Thismakes it possible to produce the gas filter of the invention or thecomposite material by a continuous process.

[0062] In a further, particular embodiment of the process of theinvention it can be advantageous to apply a ceramic or inorganic layerto a support which may be a composite material or a composite materialproduced by the process of the invention. This can be carried out, forexample, by laminating a green (unsintered) ceramic layer or aninorganic layer which is, for example, present on an auxiliary film ontothe support or by treating the composite material with a furthersuspension as described above. This composite can be strengthened byheating, e.g. by means of infrared radiation or a furnace.

[0063] The green ceramic layer used preferably comprises nanocrystallinepowder of at least one semimetal oxide or metal oxide such as aluminumoxide, titanium dioxide or zirconium dioxide. The green layer can alsocomprise an organic binder.

[0064] The use of a green ceramic layer makes it readily possible toprovide the composite material of the invention with an additionalceramic layer which, depending on the size of the nanocrystalline powderused, restricts the material permeability of the composite materialproduced in this way to very small particles.

[0065] The green layer preferably comprises nanocrystalline powderhaving a particle size of from 1 to 1000 nm. If nanccrystalline powderhaving particle sizes of from 1 to 1 nm is used, the composite materialof the invention to which an additional ceramic layer has been appliedhas a material permeability for particles having a size whichcorresponds to that of the particle size of the powder used. Ifnanocrystalline powder having a size above 10 nm is used, the ceramiclayer is permeable to particles which are half the size of the particlesof the nanocrystalline powder used.

[0066] The application according to the invention of at least onefurther inorganic layer or ceramic layer gives a composite material ofthe invention which has a pore gradient. In addition, multipleapplication of a layer makes it possible to produce composite materialshaving a particular pore size using even those supports whose pore sizeor mesh opening is not suitable for producing a gas filter or compositematerial having the required pore size. This may be the case, forexample, when a gas filter or composite material having a core size of0.25 μm is to be produced using a support having a mesh opening of above300 μm. To obtain such a gas filter or composite material, it can beadvantageous to first apply to the support at least one suspension whichis suitable for treating supports having a mesh opening of 300 μm and tosolidify this suspension after application. The composite materialobtained in this way can then be used as a support having a lower meshopening or pore size. It is possible to apply to this support, forexample, a further suspension which comprises, for example, a compoundhaving a particle size of 0.5 μm.

[0067] The crack insensitivity of composite materials having large meshopenings or pore sizes can also be improved by applying suspensionswhich comprise at least two suspended compounds to the support. Ascompounds to be suspended, preference is given to using compounds whichhave a particle size ratio of from 1:1 to 1:10, particularly preferablyfrom 1:1. to 1:2.5. The proportion by weight of the particle sizefraction hating the smaller particle size should not exceed a portion ofat most 50%, preferably 20% and very particularly preferably 10%, of thetotal weight of the particle size fractions used.

[0068] Despite the application of an additional ceramic layer orinorganic layer, which may comprise catalytically active components, tothe support, the composite material of the invention can be bendable.

[0069] The gas filter of the invention or the composite material canalso be produced by laying a support, which may, for example, be acomposite material or another suitable support material, onto a secondsupport which may consist of the same material as the first support or adifferent material or of two supports having a different materialpermeability or porosity. A spacer, a drainage material or anothermaterial suitable for conducting away materials, e.g. a compositefabric, can be laid between the two support materials. The edges of thetwo supports are joined together, for example by soldering, welding oradhesive bonding. Adhesive bonding can be carried out using commercialadhesives or adhesive tape. The suspension can be applied in the mannerdescribed above to the composite support prepared in this way.

[0070] In a particularly preferred embodiment, the superposed supportsbetween which at least one spacer, a drainage material or the like maybe arranged can be rolled up before or after, preferably after, thejoining of the edges of the supports. The spacing between two compositesupports which become juxtaposed on rolling-up can be influenced by useof thick or thin adhesive tapes for joining the edges of the supports. Asuspension as described above can be applied to such rolled-up compositesupports by, for example, dipping into a suspension. The compositesupport can be freed of excess suspension by means of compressed airafter dipping. The suspension applied to the composite support can besolidified as described above. A gas filter or composite materialproduced in this way can be used as gas filter in a rolled module. In afurther particular embodiment of the process of the invention, thecomposite support mentioned can also be produced by unrolling twosupports and, if provided, at least one spacer from individual rolls andthen laying them on top of one another. The edges of the supports canagain be joined by soldering, welding, adhesive bonding or by othersuitable methods of joining flat bodies. The suspension can then beapplied to the composite support produced in this way. The applicationof the suspension can be carried out, for example, by spraying orpainting the composite support with the suspension or by conveying thecomposite support through a bath in which the suspension is present. Theapplied suspension is solidified by one of the abovementioned methods.The composite material produced in this way can be wound onto a roll. Afurther suspension of a further inorganic layer can be applied to and/orintroduced into such a material by repeated application andsolidification. The use of different suspensions enables the materialproperties to be set as desired or according to the intended use. Notonly further suspensions but also unsintered ceramic and/or inorganiclayers which are obtainable by laminating-on as described above can beapplied to this composite material. This embodiment of the process ofthe invention can be carried out continuously or batchwise, preferablycontinuously. A composite material produced in this way can be used asgas filter in a flat module.

[0071] The support in the gas filter or composite material can,depending on the support material used, be removed again so as to form aceramic material which no longer contains any support material. If thesupport material used is, for example, a natural material such as acotton nonwoven, this can be removed from the composite material byoxidation in a suitable reactor. If a metal, e.g. iron, has been used assupport material, this support can be dissolved out of the compositematerial by treating the composite material with acids, preferably withconcentrated hydrochloric acid. If the support material additionallycomprised zeolite, flat zeolite bodies can be produced in this way.

[0072] It can be advantageous to use the composite material as supportfor the production of a gas filter or composite material according tothe invention. In a particular embodiment of the process of theinvention, it is possible, after solidification of the suspension orceramic or inorganic layer on and/or in the support material, to treatthe dried and strengthened gas filter or composite material with asolution comprising at least one metal compound, preferably a metal saltsuch as RhCl₃. The treatment can comprise, for example, spraying,painting or rolling the solution comprising a metal compound onto thecomposite material or, for example, dipping the composite material intoa solution comprising a metal compound. The gas filter or compositematerial which has been treated in this way is dried by heating. Heatingcan be carried out as indicated above. The metal compound which ispresent in and on or in or on the composite material after applicationand drying of the solution is reduced to the metal. It can beadvantageous to reduce a metal compound present in and/or on thecomposite material to the metal using a reducing agent, preferably aborohydride, very particularly preferably NaBEt₃H, LiBEt₃H, NaBMe₃H orKBPrH.

[0073] It can likewise he advantageous to reduce a metal compoundpresent on or in or else on and in the composite material to the metalby using the composite material as electrode in an electrolysis.

[0074] Catalytically active metals can also be applied in and/or on thegas filter or composite material by using a composite material without acatalytically active component as electrode in the electrolysis of asolution comprising a noble metal salt. Here, it is necessary for thecomposite material to comprise at least TiO as an inorganic componentand at least one partially electrically conductive support. Onapplication of a voltage of, for example, from 2 to 3 volt, thecomposite material becomes electrically conductive due to formation oftitanium suboxide, which is electrically conductive. As a result of theelectrolysis, catalytically active noble metal, preferably in the formof very fine particles, deposits in and/or on the composite material orgas filter.

[0075] This makes it possible to produce gas filters which comprisemetals and/or noble metals as catalytic components.

[0076] It is also possible to use the gas filter or composite materialof the invention as support for producing a gas filter according to theinvention.

[0077] In a particular variant for producing the gas filter of theinvention, at least one material-permeate composite material isintroduced, preferably rolled or folded, into a container having atleast two openings.

[0078] The composite material is preferable fixed in the container,preferably by welding, soldering or adhesive bonding, so-that a gasflowing through the filter has to pass through the composite material atleast once. The support in the composite material of the gas filter ispreferable connected to at least one power lead.

[0079] It can be advantageous to combine preferred embodiments of theprocess of the invention with at least one further preferred embodimentof the process of the invention. It may likewise be advantageous tocombine preferred embodiments of the gas filter of the invention with atleast one further preferred embodiment of the gas filter of theinvention. With knowledge of the present invention, a person skilled inthe art will be able to see further embodiments of the process of theinvention, the gas filter of the invention and/or further possible usesof the process of the invention or the gas filter of the invention. Thegas filter of the invention can be used for cleaning gases, inparticular waste gases or feed gases, and very particularly preferablygases containing at least one solid.

[0080] The gas filters of the invention are preferable used for cleaningwaste gases from power stations or for cleaning the exhaust gases fromvehicles driven by internal combustion engines. The gas filter of theinvention is very particularly preferably used for cleaning the exhaustgases from vehicles driven by diesel engines.

[0081] The following examples describe the process of the invention forproducing a gas filter according to the invention, without the processbeing restricted to these examples.

EXAMPLE 1

[0082] A suspension comprising 25 g of zirconium isopropoxide washydrolyzed with 20 g of water. The resulting precipitate wassubsequently treated with about 40 g of 25% strength nitric acid and,after the precipitate had dissolved completely, 60 g of aluminum oxideAl6SG from Alcca) were added. This suspension as stirred until allagglomerates had completely dissolved and was applied in a thickness of60 μm to a square-weave mesh of stainless steel having a mesh opening of0 μm. This composite was exposed to air at 450° C. for 3 seconds and wasdried and solidified in this way.

[0083] The composite material obtained in this way was used for gasfiltration. The present composite material is suitable, when installedin a gas filter, for filtering exhaust gases from diesel engines, sincesolid particles having a size of upward from 0.25 μm are selectivelyretained. The solid particles having a size of greater than 0.25 μmwhich are filtered out gradually block the filter during use.Application of a voltage to the support of the composite materialenables the filter or the composite material to be heated so thatparticles able to be destroyed thermally can be removed from the filterby means of oxidation reactions.

EXAMPLE 2

[0084] A Pt/Rh catalyst is incorporated on and in a composite materialas produced and described in Example 1. For this purpose, a suspensioncomprising a zirconium oxide sol which had been prepared by hydrolyzing25 g of zirconium isopropoxide with 20 g of water and subsequentlytreating the resulting precipitate with 410 g of 25 strength nitric acidand contained he Pt/Rh catalyst in a concentration of 1 was applied onand in the composite material as support. Solidification of thesuspension by heating the composite by means of air at 450° C. for 3seconds gave a composite material which is suitable for use as or in agas filter.

[0085] This gas filter, too, is very useful for the filtration of gasescontaining solid particles. The solid particles having a size of greaterthan 0.25 μm which are filtered out gradually block the filter duringuse. Application of a voltage to the support of the composite materialenables the filter or the composite material to be heated so thatparticles able to be destroyed thermally can be removed from the filter.

[0086] When the filter has reached a suitable process temperature atwhich the oxidatively decomposable solids can be destroyed catalyticallyby oxidation reactions owing to the presence of the Pt/Rh catalyst, thesolids which have been filtered cut are continually destroyed byoxidation, resulting in considerably reduced blockage of the gas filter.In this embodiment of the gas filter of the invention, energy does nothave to be consumed continually for regeneration of the filter, but itis sufficient for the gas filter to be heated at least once during thestart-up or running-up phase. Once the reaction in and on the filter isproceeding, the energy liberated in the destruction of the solidparticles generates the high temperatures necessary for regeneration ofthe filter.

1. A regenerable gas filter for filtering gases which comprises acomposite material based on at least one open-structured andmaterial-permeable support and having on at least one side of thesupport and in the interior of the support at least one inorganiccomponent which comprises essentially at least one compound of a metal,a semimetal or a mixed metal with at least one element of main groupsIII to VII.
 2. A regenerable gas filter which comprises a compositematerial which is obtainable by application of a suspension whichcomprises at least one inorganic component comprising compound of atleast one metal, a semimetal or a mixed metal with at least one elementof main groups III to -VII and a sol to an open-structured andmaterial-permeable support and by subsequent heating at least onceduring which the suspension comprising at least one inorganic componentis solidified on or in or on and in the support.
 3. A gas filter asclaimed in at least one of claims 1 and 2, wherein the compositematerial or the gas filter is permeable to gases, solids or liquids. 4.A gas filter as claimed in at least one of claims 1 to 3, wherein theopen-structured and material-permeable support has intermediate spaceshaving a size of from 0.02 to 500 μm.
 5. A gas filter as claimed in atleast one of claims 1 to 4, wherein the support comprises at least onematerial selected from the group consisting of carbon, metals, alloys,glass, ceramics, minerals, plastics, amorphous substances, naturalproducts, composite materials or at least one combination of thesematerials.
 6. A gas filter as claimed in at least one of claims 1 to 5,wherein the support comprises at least woven, felted or ceramicallybound fibers or at least sintered spheres or particles.
 7. A gas filteras claimed in at least one of claims 1 to 6, wherein the supportcomprises at least one at least partially electrically conductivematerial.
 8. A gas filter as claimed in at least one of claims 1 to 7,wherein the support is perforated.
 9. A gas filter as claimed in atleast one of claims 1 to 8, wherein the material-permeable support hasbeen made material-permeable by laser treatment or ion beam treatment.10. A gas filter as claimed in at least one of claims 1 to 9, whereinthe support comprises fibers of at least one material selected from thegroup consisting of carbon, metals, alloys, ceramics, glass, plastics,composite materials, minerals or fibers of at least one combination ofthese materials.
 11. A gas filter as claimed in at least one of claims 1to 10, wherein the support comprises woven fibers of metal or alloys.12. A gas filter as claimed in at least one of claims 1 to 11, whereinthe support comprises at least one woven steel mesh.
 13. A gas filter asclaimed in at least one of claims 1 to 12, wherein the support comprisesat least one woven mesh having a mesh opening of from 5 to 500 μm.
 14. Agas filter as claimed in at least one of claims 1 to 13, wherein thesupport comprises at least one expanded metal having a mesh opening offrom 5 to 500 μm.
 15. A gas filter as claimed in at least one of claims1 to 14, wherein the support comprises a sintered metal, a sinteredglass or a metal nonwoven having a pore width of from 0.1 to 500 μm. 16.A gas filter as claimed in at least one of claims 1 to 15, wherein thesupport comprises at least aluminum, silicon, cobalt, manganese, zinc,vanadium, molybdenum, indium, lead, bismuth, silver, gold, nickel,copper, iron, titanium, platinum, stainless steel, steel or brass or analloy of these materials or a material coated with Au, Ag, Pb, Ti, Ni,Cr, Pt, Pd, Rh, Ru and/or Ti.
 17. A gas filter as claimed in at leastone of claims 1 to 16, wherein the inorganic component comprising atleast one compound of at least one metal, semimetal or mixed metal withat least one element of main groups III to VII or at least one mixtureof these compounds comprises at least one compound of the transitionelements and of main groups III to VII or at least one compound of thetransition elements and at least one compound of main groups III to VII,with the compounds having a particle size of from 0.01 to 25 μm.
 18. Agas filter as claimed in at least one of claims 1 to 17, wherein theinorganic component comprising a compound of at least one metal, atleast one semimetal or at least one mixed metal with at least oneelement of main groups III to VII or a mixture of these compoundscomprises at least one compound of an element of transition groups IIIto VIII or at least one element of main groups III to V with at leastone of the elements Te, Se, S, 0, Sb, As, P, N, Ge, Si, C, Sa, Al or Bor at least one compound of an element of transition groups III to VIIIand at least one element of main groups III to V with at least one ofthe elements Te, Se, S, 0, Sb, As, P, N, Ge, Si, C, Ga, Al or B or amixture of these compounds.
 19. A gas filter as claimed in at least oneof claims 1 to 18, wherein the inorganic component comprises at leastone compound of at least one of the elements C, Y, Ti, Zr, V, Cr. Mo, W,Fe, Co, B, Al, In, Tl, Si, Ge, Sn, Pb, Sb or Bi with at least one of theelements Te, Se, S, O, Sb, As, P, N, C or Ga or at least one of theseelements.
 20. A gas filter as claimed in at least one of claims 1 to 19,wherein the inorganic component comprises aluminosilicates, aluminumphosphates, zeolites or partially: exchanged zeolites.
 21. A gas filteras claimed in at least one of claims 1 to 20, wherein the inorganiccomponent comprises amorphous microporous mixed oxides which may containup to 20% of non-hydrolyzable organic compounds.
 22. A gas filter asclaimed in at least one of claims 1 to 21, wherein the inorganiccomponent comprises at least aluminum oxide or titanium oxide.
 23. A gasfilter as claimed in at least one of claims 1 to 22, wherein thecomposite material comprises at least two particle size fractions of atleast one inorganic component.
 24. A gas filter as claimed in claim 23,wherein the particle size fractions in the composite material have aparticle size ratio of from 1:1 to 1:100.
 25. A gas filter as claimed inat least one of claims 23 and 24, wherein the composite material has aratio of amounts of the particle size fractions of from 0.01:1 to1:0.01.
 26. A gas filter as claimed in at least one of claim 1 to 25,wherein the composite material comprises particle size fractions havingan average particle size of from 0.3 to 3 μm.
 27. A gas filter asclaimed in at least one of claims 1 to 26, wherein the materialpermeability of the composite material can be limited to particleshaving a particular maximum size by means of the particle size of theinorganic component used.
 28. A gas filter as claimed in at least one ofclaims 1 to 27, wherein the composite material has pores which arepermeable to particles having a maximum size of from 0.1 to 0.5 μm. 29.A gas filter as claimed in at least one of claims 1 to 28, wherein thecomposite material is bendable.
 30. A gas filter as claimed in claim 29,wherein the composite material can be bent to a radius of down to 2 μm.31. A gas filter as claimed in at least one of claims 1 to 30, whereinthe gas filter has the composite material rolled into a suitablecontainer having at least one gas inlet and at least one gas outlet,with the composite material being arranged so that the gas to befiltered must, after entering the gas filter, pass at least once throughthe composite material before it can leave the gas filter via the gasoutlet.
 32. A gas filter as claimed in at least one of claims 1 to 31,wherein thermally decomposable solids or liquids which have beenfiltered from a filtered gas and block the pores of the compositematerial are removed from the gas filter by baking the gas filter byapplication of a voltage to the support of the composite material.
 33. Agas filter as claimed in at least one of claims 1 to 32, wherein the gasinlet and the gas outlet are provided with a flow- or pressure-measuringdevice by means of which the pressure or the amount of gas entering andleaving the filter is measured and when a preset difference between themeasured values, which represents a measure of the blocking of thecomposite material, is reached, the baking of the gas filter iscommenced.
 34. A gas filter as claimed in at least one of claims 1 to33, wherein the composite material comprises at least one catalyticallyactive component.
 35. A gas filter as claimed in claim 34, wherein thecomposite material comprises, as catalytically active component, atleast one inorganic material, at least one metal or at least oneorganometallic compound which has catalytically active centers on itssurface.
 36. A gas filter as claimed in claim 34, wherein the compositematerial comprises, as catalytic component, a zeolite, silicalite or anamorphous microporous mixed oxide.
 37. A gas filter as claimed in claim34, wherein the composite material comprises, as catalytically activecomponent, at least one oxide of at least one of the elements Mo, Sn,Zn, V, Mn, Fe, Co, Ni, As, Sb, Pb, Bi, Ru, Re, or, W, Nb, Hf, La, Ce,Gd, Ga, In, Tl, Ag, Cu, Li, K, Na, Be, Mg, Ca, Sr and Ba.
 38. A gasfilter as claimed in claim 34, wherein the composite material comprisesat least titanium suboxide as catalytically active component.
 39. A gasfilter as claimed in claim 34, wherein the composite material comprises,as catalytically active component, at least one metal compound selectedfrom among the compounds of the metals Pt, Rh, Ru, Ir, Au, Ag, Os, Re,Cu, Ni, Pd and Co.
 40. A gas filter as claimed in claim 34, wherein thecomposite material comprises, as catalytically active component, atleast one metal selected from among the metals Pt, Rh, Ru, Ce, Ir, Au,Ag, Os, Re, Cu, Ni, Pd and Co.
 41. A process for producing a gas filteras claimed in any of claims 1 to 40, which comprises producing amaterial-permeable composite material by applying, in and on at leastone open-structured and material-permeable support, at least onesuspension which comprises at least one inorganic component comprisingat least one compound of at least one metal, a semimetal or a mixedmetal with at least one of the elements of main groups III to VII and asol and by solidifying the suspension on or in or on and in the supportmaterial by subsequent heating at least once.
 42. The process as claimedin claim 41, wherein the suspension is applied on and in or else on orin the support by printing, pressing-on, pressing-in, rolling-on, doctorblade coating, painting-on, dipping, spraying or casting.
 43. Theprocess as claimed in at least one of claims 41 and 42, wherein anopen-structured and material-permeable support comprising a materialselected from the group consisting of carbon, metals, minerals, ceramic,composite materials or at least one combination of these materials isused.
 44. The process as claimed in at least one of claims 41 to 43,wherein the support comprises at least one material which is at leastpartially electrically conductive.
 45. The process as claimed in atleast one of claims 41 to 44, wherein a woven stainless steel mesh isused as support.
 46. The process as claimed in at least one of claims 41to 45, wherein the suspension which comprises at least one inorganiccomponent and at least one metal oxide sol, at least one semimetal oxidesol or at least one mixed metal oxide sol or a mixture of these sols isproduced by suspending at least one inorganic component in at least oneof these sols. 47 The process as claimed in at least one of claims 41 to46, wherein the suspension comprises at least one catalytically activecomponent.
 48. The process as claimed in at least one of claims 41 to47, wherein the sols are obtained by hydrolyzing at least one metalcompound, a mixed metal compound or at least one semimetal compoundusing a liquid, a gas or a solid.
 49. The process as claimed in claim48, wherein the liquid, gas or solid used for hydrolyzing the metalcompound is water, water vapor, ice, alcohol or an acid or a combinationof these compounds.
 50. The process as claimed In at least one of claims48 and 9, wherein the compound to be hydrolyzed is added prior to thehydrolysis to alcohol or an acid or a combination of these alcohol or anacid or a combination of these liquids.
 51. The process as claimed in atleast one of claims 48 to 50, wherein at least one metal nitrate, ametal chloride, a metal carbonate, a metal alkoxide compound or at leastone semimetal alkoxide compound is hydrolyzed.
 52. The process asclaimed in claim 51, wherein at least one metal alkoxide compound or atleast one semimetal alkoxide compound selected from among the alkoxidecompounds of the elements Ti, Zr, Al, Si, Sn, Ce and Y or a metalnitrate, a metal chloride or a metal carbonate selected from among themetal salts of the elements Ti, Zr, Al, Si, Sn, Ce and Y is hydrolyzed.53. The process as claimed in claim 52, wherein a titanium alkoxidecompound is hydrolyzed.
 54. The process as claimed in at least one ofclaims 41 to 53, wherein the hydrolysis of the compounds to behydrolyzed is carried out using at least half the molar ratio of water,based on the hydrolyzable group of the hydrolyzable compound.
 55. Theprocess as claimed in at least one of claims 41 to 54, wherein thehydrolyzed compound is treated with at least one organic or inorganicacid.
 56. The process as claimed in claim 55, wherein the organic orinorganic acid has a concentration of from 10 to 60%.
 57. The process asclaimed in at least one of claims 55 and 56, wherein the hydrolyzedcompound is treated with at least one mineral acid selected from thegroup consisting of nitric acid, sulfuric acid, perchloric acid andhydrochloric acid or a combination of these acids.
 58. The process asclaimed in at least one of claims 41 to 57, wherein a titanium dioxidesol acidified with mineral acid is used as sol.
 59. The process asclaimed in at least one claims 41 to 58, wherein at least one inorganiccomponent having a particle size of from 1 to 10,000 nm is suspended ina sol.
 60. The process as claimed in claim 59, wherein an inorganiccomponent comprising at least one compound selected from among metalcompounds, semimetal compounds, mixed metal compounds and metal mixedcompounds with at least one of the elements of main groups III to VII,or at least one mixture of these compounds, is suspended.
 61. Theprocess as claimed in at least one of claims 59 and 60, wherein aninorganic component comprising at least one compound from among theoxides of the transition elements or the elements of main groups III toV is suspended.
 62. The process as claimed in claim 61, wherein theoxides are selected from among the oxides of the elements Sc, Y, Ti, Zr,V, Nb, Cr, Mo, W, Mn, Fe, Co, B, Al, In, Tl, Si, Ge, Sn, Pb and Bi. 63.The process as claimed in at least one of claims 41 to 62, wherein atleast one inorganic component used is aluminum oxide having a particlesize of from 0.3 to 3 μm.
 64. The process as claimed in at least one ofclaims 41 to 63, wherein at least one catalytically active component isincorporated into the composite material.
 65. The process as claimed inat least one of claims 41 to 64, wherein at least one catalyticallyactive component is added to the sol.
 66. The process as claimed in atleast one of claims 41 to 65, herein at least one catalytically activecomponent having a particle size of from 1 to 10,000 nm is suspended ina sol.
 67. The process as claimed in at least one of claims 65 and 66,wherein at least one catalytically active component comprises at leastone compound selected from among metal compounds, semimetal compounds,mixed metal compounds and metal mixed compounds with at least one of theelements of main groups III to VII or organic compounds or at least onemixture of these compounds.
 68. The process as claimed in at least oneof claims 41 to 67, wherein at least one noble metal, a noble metalcompound or a zeolite is incorporated as catalytic component into thecomposite material.
 69. The process as claimed in at least one of claims41 to 68, wherein at least one catalytically active component comprisesat least one compound selected from the group consisting of zeolite,silicalite or amorphous mixed oxide.
 70. The process as claimed in atleast one of claims 41 to 69, wherein the proportion by mass of thesuspended components corresponds to from 0.1 to 500 times the hydrolyzedcompound used.
 71. The process as claimed in at least one of claims 41to 70, wherein the suspension present on and in or else on or in thesupport is solidified by heating the composite at least once at from 50to 1000° C.
 72. The process as claimed in claim 71, wherein thecomposite is subjected to a temperature of from 50 to 100° C. for from10 minutes to 5 hours.
 73. The process as claimed in claim 71, whereinthe composite is subjected to a temperature of from 100 to 800° C. forfrom 1 second to 10 minutes.
 74. The process as claimed in at least oneof claims 71 to 73, wherein heating is carried out by means of heatedair, hot air, infrared radiation, microwave radiation or electricallygenerated heat.
 75. The process as claimed in at least one of claims 71to 73, wherein heating is carried out using the support material aselectrical resistance heating element.
 76. The process as claimed in atleast one of claims 41 to 75, wherein the solidification of thesuspension is achieved by applying the suspension on and in a preheatedsupport.
 77. The process as claimed in at least one of claims 41 to 76,wherein at least one support is unwound from a roll, passed at a speedof from 1 to 50 m/h through at least one apparatus which applies thesuspension on or in or on and in the support and at least one furtherapparatus which makes possible the solidification of the suspension onor in or on and in the support by heating and the composite materialproduced in this way is wound up on a second roll.
 78. The process asclaimed in at least one of claims 41 to 77, wherein an unsinteredceramic or inorganic layer is applied to a support and is strengthenedby heating.
 79. The process as claimed in at least one of claims 41 to78, wherein the dried and strengthened composite material impregnatedwith a solution comprising at least one metal salt, the compositematerial which has been treated in this way is dried by heating and themetal salt which is present in and on or else in or on the compositematerial is reduced to metal.
 80. The process as claimed in at least oneof claims 41 to 79, wherein a metal salt which is present in thecomposite material is reduced to metal by treating the compositematerial with a reducing agent.
 81. The process as claimed in claim 50,wherein the reducing agent used is a borohydride.
 82. The process asclaimed in at least one of claims 41 to 81, wherein a metal salt whichis present in or on or else in and on the composite material is reducedto metal by using the composite material as electrode in anelectrolysis.
 83. The process as claimed in at least one of claims 41 to82, wherein a material-permeable composite material is introduced into acontainer having at least two openings.
 84. The process as claimed inclaim 83, wherein the composite material is introduced into folded orrolled form in the container.
 85. The process as claimed in at least oneof claims 41 to 84, wherein the composite material is fixed in thecontainer so that a gas flowing through the filter has to pass throughthe composite material at least once.
 86. The process as claimed inclaim 8, wherein the composite material is fixed in the container bywelding, soldering or adhesive bonding.
 87. The process as claimed in atleast one of claims 41 to 86, wherein the support in the compositematerial is connected to at least one power lead.
 88. The use of a gasfilter as claimed in at least one of claims 1 to 40 for cleaning wasteor feed gases.
 89. The use of a gas filter as claimed in at least one ofclaims 1 to 40, for cleaning waste gases from power stations.
 90. Theuse of a gas filter as claimed in at least one of claims 1 to 40 forcleaning the exhaust gases of vehicles driven by internal combustionengines.
 91. The use of a gas filter as claimed in at least one ofclaims 1 to 40 for cleaning the exhaust gases of vehicles driven bydiesel engines.